Multi-lumen catheter with separate distal tips

ABSTRACT

A multi-lumen catheter including tip sections distal to a dividing point, the tip sections releasably joined by a method that produces a variable separation force between the tip sections along a length thereof. An increasing separation force may be imparted to the tip sections by providing an increasing bond strength in fusion zones from a distal portion of the tip sections toward the dividing point.

PRIORITY

This application is a division of U.S. patent application Ser. No.10/371,774, filed Feb. 21, 2003, which is incorporated by reference intothis application as if fully set forth herein.

FIELD OF THE INVENTION

The present invention relates generally to a multi-lumen catheter havinga plurality of separate distal tips and more particularly to an improvedsplit-tip catheter.

BACKGROUND OF THE INVENTION

Multi-lumen catheters are used for the purpose of creating two or moreseparate fluid pathways, such as in hemodialysis applications. A primarygoal of hemodialysis access is to provide a reliable and effective meansof dialysis, which means that a sufficient volume of blood over a periodof time must be removed from and returned to the patient. Because thecontaminated and cleansed blood must be kept separate for an effectivedialysis procedure, a dual lumen catheter is generally used. These duallumen catheters are usually configured so that there is a shorter lumenthat aspirates blood from a blood vessel of a patient to a dialysismachine where it is processed for the removal of toxins, and a longerlumen that infuses the purified blood to the patient. The shorter lumenutilized for aspiration is generally referred to as the “arteriallumen,” while the longer lumen utilized for infusion is generallyreferred to as the “venous lumen.” The reason for the different lengthsis to minimize co-mingling of aspirated and infused blood.

The primary problems occurring in dual lumen dialysis catheters areblood clotting (thrombosis) and fibrin (the protein formed during normalblood clotting that is the essence of the clot) sheath formation.Thrombus and fibrin sheath formation can occlude distal tips of thedialysis catheter lumens, resulting in loss of catheter function whensuch an occlusion prevents blood flow. This typically occurs initiallyin the arterial lumen used for aspiration of blood from a patient. Asecondary problem relates to the arterial lumen “sucking” against thevessel wall, in which the arterial lumen openings become fully occludedby the patient's vasculature.

To specifically address these problems, a new type of dialysis accesscatheter has been designed that utilizes independent “free floating”distal tip sections that separate at a distal end of the catheter totheoretically reduce the likelihood of potential occlusion and “sucking”during dialysis treatment. U.S. Pat. No. 6,001,079 to Pourchez and U.S.Pat. Nos. 5,947,953 and 6,190,349 to Ash et al., all incorporated byreference herein, are directed to said new type of catheter, hereinafterreferred to as a “split-tip catheter.”

Catheters used for hemodialysis are generally inserted according tostandard technique. This includes identifying the location of thecentral veins in which the catheter is to be inserted, utilizing theSeldinger technique to cannulate the central vein with a guidewire, andpassing various instruments over the guidewire until the catheter is inplace. In the case of a small diameter catheter made of relatively stiffmaterial (i.e., a percutaneous catheter for acute access), the catheteritself can be passed over the guidewire and into the central vein. Inthe case of a larger diameter catheter, the passage to the central veinmust be widened through the use of dilator(s), after which the cathetercan be passed over the guidewire. Another possibility available to thephysician is to use an introducer sheath, which is passed over theguidewire (after dilation or simultaneously therewith) forming a pathfor the catheter to access the central vein.

Due to the configuration of the split-tip catheter, standard insertiontechniques must be modified. With respect to non-sheath insertions, theseparate distal tip sections must each be passed over the guidewire toensure their arrival at the targeted central vein without attendantproblems. Suggested means for accomplishing this (in a dual lumencatheter) is to pass the back end of the guide wire through the distalend hole of one tip section and out a side hole thereof into the distalend hole of the other tip section (Patel et al., J. Vasc. Interv.Radiol. (2001), vol. 12, pages 376-378). However, such a method canbecome problematic depending on the placement of the side holes and, infact, may be impossible in the event that no side holes are provided.With respect to sheathed insertions, the separate distal tip sectionsmay tend to flare outward and catch or “snag” on the inner wall of thedelivery sheath thereby preventing smooth delivery of the catheter tothe central vein.

There is a need for improvements to split-tip catheters and newconfigurations thereof, which enhance the design and further alleviateconcerns with regard to typical problems encountered in hemodialysiscatheters. There is also a need for new configurations and new methodsfor insertion of split-tip catheters to overcome problems associatedtherewith

SUMMARY OF THE INVENTION

In accordance with the present invention, several embodiments aredescribed, which may be improvements to prior art split-tip catheters ormay be novel catheter embodiments heretofore undisclosed. As usedherein, the following terms have the following meanings:

“Split-tip catheter” refers to a catheter having a body enclosing atleast two lumens and a dividing point that separates at least two tipsections from one another distal thereto, each of the tip sectionsenclosing at least one lumen and being separated or separable from oneanother along their length.

“Dividing point” refers to a point along the length of the split-tipcatheter distal to which at least two tip sections are separated or areseparable from one another.

“Tip section” refers to a portion of the split-tip catheter, enclosingat least one lumen, which is separable or is separated from another tipsection along its length distal to a dividing point.

“Inner surface” refers to a surface on a tip section that is facing oradjacent a companion tip section (a tip section that separates or isseparable distal to the same dividing point).

“Outer surface” refers to a surface on a tip section that is not facinga companion tip section.

“Separation force” refers to a force required to separate the tipsections from one another.

“Excessive separation force” refers to a force required to separate thetip sections from one another, which is too great to be consideredpractical for a clinician in a typical setting. By definition, anexcessive separation force is required to separate the tip sections ofthe split tip catheter from one another proximal to the dividing point.

“Cylindrical” is used according to its ordinary meaning (i.e., a shapehaving a constant circular cross-section).

One improvement to prior art split-tip catheters comprises a uniqueconfiguration of each tip section to improve flow characteristics,provide ease of delivery and overcome typical problems associated withhemodialysis catheters. In a dual lumen embodiment, the split-tipcatheter comprises a shorter arterial tip section comprising asemi-cylindrical shape with a rounded distal end, and a longer venoustip section comprising a semi-cylindrical shape in a proximal portionwhich smoothly transitions in a transition region to a cylindrical shapein a distal portion, the cross-sectional size of the distal portionbeing greater than the cross-sectional size of the proximal portion, thedistal portion terminating in an inward bevel. Another improvementcomprises the strategic placement of openings placed on the tip sectionsof the split-tip catheter. With particular respect to an arterial tipsection in a dual lumen configuration, the openings are offset bothlongitudinally and circumferentially so that full 360° fluid flow isrealized and problems related to “sucking” against the vessel wall aremitigated.

Another improvement to the prior art split-tip catheters comprises ameans for reducing dead space on the surface of the tip sections of asplit-tip catheter in the region of separation, which includes, but isnot limited to, an opening or openings located on an inner surface ofone or more tip sections near a dividing point of the split-tipcatheter. In one embodiment of the invention, a hole or opening ispositioned on an aspirating lumen tip section. In another embodiment ofthe invention, a hole or opening is positioned on an infusion lumen tipsection. In each of these embodiments, there could be multiple holes oropenings on the lumen tip sections. Additionally, the hole(s) oropening(s) could be positioned in many different locations along thelength of the tip sections and/or catheter.

An additional improvement to prior art split-tip catheters is related tothe delivery thereof either with or without the use of a deliverysheath. With respect to a non-sheathed delivery, the improvementconcerns strategic placement of a guidewire opening in the distal end ofthe venous tip section so that the guidewire is easily passed throughthe venous tip section and into the arterial tip section. With respectto a sheathed delivery, the improvement relates to a friction-reducingmeans for reducing friction between the catheter and a delivery sheath.As discussed above, movement of the delivery sheath with respect to thesplit-tip catheter can result in the inside surface of the deliverysheath engaging the tip sections, which can cause tears in the deliverycatheter, problems in the delivery process and other unwantedoccurrences.

Thus, in one embodiment of the invention, a bump or protrusion ofmaterial is positioned on the outer surface of one or more tip sectionsadjacent the inside surface of the delivery sheath. In anotherembodiment of the invention, a ring of material is positioned around theend of one or more tip sections. In yet another embodiment of theinvention, an inflatable material is positioned on the outer surface ofthe catheter in one or more locations to be inflated during delivery toprovide a buffer zone for prevention of direct contact of the tipsections with the inside surface of the delivery sheath. Followingdelivery of the split-tip catheter, said material would be deflated. Instill another embodiment, bumps or protrusions of material arepositioned on the inside surface of the sheath.

With respect to prior art split-tip catheters that are releasably joinedor “splittable,” an improvement is described in which tip sections thatare initially joined together distal to a dividing point can beseparated along a predetermined length thereof upon an application of aparticular separation force. In this aspect of the invention, theseparation force required to disjoin the tip sections varies along thelength of the tip sections (in the described embodiments the separationforce increases from the distal end to the proximal end of the catheter)as the bond between the tip sections is varied.

Thus, in one embodiment, the splittable tip sections are releasablyjoined to one another distal to a dividing point, enabling split andjoined configurations to be interchangeable. In another embodiment ofthe invention, the bond between the splittable tip sections varies in acontinuous fashion along their length in such a way that the forcerequired to separate them is progressively increased in a straight linefashion as measured from a distal end of the tip sections to thedividing point. In yet another embodiment of the invention, the requiredseparation force increases in incremental steps as measured from adistal end of the tip sections to the dividing point. In each of theseembodiments, while the tip sections are splittable along a predeterminedlength of the catheter distal to a dividing point, it should beappreciated that said dividing point is a fixed point beyond whichseparation can not take place without use of excessive separation force.

These and other embodiments, features and advantages of the presentinvention will become more apparent to those skilled in the art whentaken with reference to the following more detailed description of theinvention in conjunction with the accompanying drawings that are firstbriefly described

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a split-tip catheter according to thepresent invention.

FIG. 2 is a perspective view of an alternate embodiment of a split-tipcatheter according to the present invention.

FIG. 3 is a close-up view of the tip sections of the split-tip catheterof FIG. 1, illustrating the positioning of openings therein.

FIG. 4 is a similar view to FIG. 3, illustrating an alternate embodimentthereof.

FIG. 5 is a perspective view of a straight version of a split-tipcatheter according to the present invention.

FIG. 6 is a perspective view of a precurved version of a split-tipcatheter according to the present invention.

FIG. 7 is a close-up view of the distal end of the split-tip catheter ofFIGS. 5 and 6.

FIGS. 8A-8G are cross-sectional views of the distal end of the split-tipcatheter of FIG. 7, taken along lines 8A-8A, 8B-8B, 8C-8C, 8D-8D, 8E-8E,8F-8F, 8G-8G, respectively.

FIG. 9 is a perspective view of FIG. 7 taken along line 9-9.

FIG. 10 is a cross-sectional view of FIG. 9, taken along line 10-10.

FIGS. 11A-11E are cross-sectional views of FIG. 10, taken along lines11A-11A, 11B-11B, 11C-11C, 11D-11D, 11E-11E, respectively.

FIG. 12 is an alternate embodiment of the split tip catheter of thepresent invention, showing a close-up view of a distal end thereof.

FIG. 13 is a perspective view of FIG. 12 taken along line 13-13.

FIG. 14 is a cross-sectional view of FIG. 13, taken along line 14-14.

FIG. 15A is an inside view of an introducer sheath containing a priorart split-tip catheter.

FIG. 15B is a close-up view of the prior art catheter of FIG. 15A,showing forces acting thereon upon delivery out of the introducersheath.

FIG. 16 is a perspective view of the tip sections of a split-tipcatheter according to one embodiment of the present invention.

FIG. 17 is a perspective view of the tip sections of a split-tipcatheter according to another embodiment the present invention.

FIG. 18 is a perspective view of the tip sections of yet anotherembodiment of a split-tip catheter according to the present invention

FIG. 19 is an inside view of an introducer sheath according to oneembodiment of the present invention.

FIG. 20 is a cross-sectional view of FIG. 11 taken along line 20-20.

FIG. 21A is a graph illustrating a continuous separation force F as afunction of position P of the tip sections.

FIG. 21B is a graph illustrating an incremental separation force F as afunction of position P of the tip sections.

FIG. 21C is a representative view of a split-tip catheter, showing oneembodiment of the present invention regarding varying separation forcerequired to separate the tip sections.

FIG. 21D is a representative view of a split-tip catheter, showinganother embodiment of the present invention regarding varying separationforce required to separate the tip sections.

FIG. 21E is a representative view of a split-tip catheter, showinganother embodiment of the present invention regarding varying separationforce required to separate the tip sections.

FIG. 21F is a representative view of a split-tip catheter, showinganother embodiment of the present invention regarding varying separationforce required to separate the tip sections.

FIG. 21G is a representative view of a split-tip catheter, showinganother embodiment of the present invention regarding varying separationforce required to separate the tip sections.

FIG. 21H is a representative view of a split-tip catheter, showinganother embodiment of the present invention regarding varying separationforce required to separate the tip sections.

FIG. 21I is a representative view of a split-tip catheter, showinganother embodiment of the present invention regarding varying separationforce required to separate the tip sections.

FIG. 22A is a representative view of a split-tip catheter, illustratinga twisted configuration according to one embodiment of the presentinvention.

FIG. 22B is a representative view of a split-tip catheter, illustratinga twisted configuration according to another embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description should be read with reference to thedrawings, in which like elements in different drawings are identicallynumbered. The drawings, which are not necessarily to scale, depictselected preferred embodiments and are not intended to limit the scopeof the invention.

The detailed description illustrates by way of example, not by way oflimitation, the principles of the invention. This description willclearly enable one skilled in the art to make and use the invention, anddescribes several embodiments, adaptations, variations, alternatives anduses of the invention, including what is presently believed to be thebest mode of carrying out the invention.

The present invention is directed to multi-lumen catheters with separatedistal tips in the form of improvements over prior art split-tipcatheters as well as new configurations and embodiments. While theexamples and embodiments of a multi-lumen catheter are discussed hereinin terms of a dialysis catheter, it should be appreciated that there aremany other possible uses for a multi-lumen catheter of the typepresented herein. Also, while a currently preferred material is medicalgrade polyurethane, it should be appreciated that a variety of suitablematerials could be utilized to form the multi-lumen catheter of thepresent invention. Importantly, the material chosen should possesscharacteristics such as flexibility, durability and relative softnessand conformability when placed within a blood vessel.

Referring now to FIG. 1, a split-tip catheter 10 is shown having aproximal end 12 and a distal end 14. The proximal end of the catheter 12is attached to a Y-connector 60, which in turn is connected to extensiontubing 62, as is standard in dialysis catheters. The catheter 10 has twolumens defined by an outer wall 16 and a bisecting planar septum 18. Thetwo lumens extend from the proximal end of the catheter 12 to the distalend of the catheter 14 and have a D-shape configuration due to theplanar septum 18. Of course, this is not the only possible configurationand certainly the lumens could assume a variety of shapes, includingcircular, crescent-shaped, oval, etc. The Y-connector 60 and extensiontubing 62 fluidly connect the lumens to a blood treatment unit ordialysis machine (not shown). The distal end 14 of the catheter 10 isseparated into tip sections 40 and 50 distal to a dividing point 30.While only two tip sections are shown in FIG. 1, it is certainlypossible for a plurality of tip sections to branch from the dividingpoint 30, depending, for example, on the number of lumens within thecatheter 10. Thus, it is contemplated that three, four or more tipsections could separate or be separable distal to the dividing point 30,corresponding to three, four or more lumens within the catheter 10.

In addition, although only one dividing point is illustrated in FIG. 1,it is contemplated that two or more could be utilized, which is shown asan alternate embodiment in FIG. 2. A multi-lumen catheter 80 has a firsttip section 82 and a second tip section 84 distal to a first dividingpoint 81 and a third tip section 86 and a fourth tip section 88 distalto a second dividing point 85 distal to the first dividing point 81along the second tip section 84. Of course, it would be possible to haveadditional dividing points and tip sections, which could accommodate anynumber of multi-lumen configurations. Referring back to FIG. 1, the twolumens of the catheter 10 continue from the proximal end 12 to thedistal end 14 into respective tip sections 40 and 50 distal to thedividing point 30. The lumens can be of equal size and shape fromproximal to distal end or can vary in one or more locations. Thus, forexample, if it was desirable to increase the flow of blood, the lumen intip section 50 could increase in cross-sectional area distal to thedividing point 30 so that blood flowing out of tip section 50 would havea reduced velocity.

Referring now to FIG. 3, the cross-sectional shape of the lumen withintip section 50 transitions from a D-shape to a circular shape, thetransition occurring distal to the end opening 44 of tip section 40.Such a configuration for the tip section 50 is optimal for many reasons,which will be explored below with reference to FIGS. 7-14. Importantly,the overall configuration for the distal end 14 of the catheter 10,including the shape of tip sections 40 and 50, has been found to beoptimal regarding delivery of the catheter into a body lumen as well aswith respect to its performance in vivo.

As shown in FIGS. 1 and 3, tip section 40 terminates in a roundedconfiguration and tip section 50 terminates in a beveled configuration,providing end openings 44 and 54 therethrough. While certainly there aremany possible degrees of angles that can be used for the bevel cutaccording to the present invention, the currently preferred range isbetween approximately 25° and 75°, while the angle shown isapproximately 45°. Of course, there are a multitude of endconfigurations possible for each tip section in addition to those shown,including blunt, tapered, curved, notched, etc. In particular, a reversebevel or notched (area removed from the end) configuration could beformed in the tip section 40 to minimize the opportunity for “sucking”against the wall of the superior vena cava or right atrium during adialysis procedure. As is standard for dialysis catheters, tip section40 is used to aspirate blood from the patient, while tip section 50 isused to infuse treated blood from a dialysis machine, as discussedabove.

FIG. 3 illustrates one of the stated improvements over the prior artsplit-tip catheters, namely the presence of an opening in closeproximity to the dividing point, by showing the tip sections of FIG. 1in more detail. Tip sections 40 and 50 distal to dividing point 30 haveinner surfaces 45 and 55 and outer surfaces 47 and 57 respectively. Inclose proximity to the dividing point 30 on inner surface 45 ispositioned an opening 46, providing an additional inlet on the tipsection 40 for the aspiration of blood. Importantly, opening 46addresses an apparent problem with certain split-tip catheter designswith respect to clotting and fibrin sheath formation at or near thedividing point. This phenomenon is likely due to the unused surface areaproximal to the arterial and venous end openings 44 and 54, whichincreases the surface area for platelet adhesion. By positioning opening46 in close proximity to the dividing point 30, blood flow therethroughacts to dislodge any clot formation on the inner surfaces 45 and 55. Inaddition, the presence of one or more openings in close proximity to thedividing point may permit slow leaching of heparin along the innersurfaces 45 and 55, which also would prevent clot formation as thecatheter lumens are flushed between dialysis treatments. As used herein,the term “close proximity” refers to a distance that is nearer thedividing point than the distal end of the subject tip section and canrefer to any point along the length of the subject tip section in thatrange.

It should be appreciated that even though one hole on inner surface 45is shown in FIG. 3, a plurality of openings are also possible and mayeven be preferable, depending on the particular application. Inaddition, although a small circular opening 46 is shown, certainly othershapes and sizes would be equally within the scope of the invention,including oval shapes, slits, etc. For example, an opening near thedividing point could comprise a valve such as that described in U.S.Pat. No. 4,549,879 to Groshong et al., which is incorporated byreference herein. By utilizing a valve, leaching may be controlled,which could be advantageous in certain situations, depending on thepatient's disposition. In an alternate embodiment, small mounds ofmaterial or protrusions 49 are positioned adjacent the opening 46 oneither side thereof as shown in FIG. 4. Of course, while two protrusions49 are shown, certainly any number of protrusions 49 are contemplated.The protrusions 49 serve at least two purposes, including maintainingseparation between the tip sections 40 and 50 and preventing opening 46from becoming occluded.

While the embodiment shown in FIG. 3 illustrates opening 46 on innersurface 45, it may instead be preferable to place one or more openingson the inner surface 55 of tip section 50. Alternatively, it may bedesirable to place one or more openings on both inner surfaces 45 and 55at similar positions or offset from one another. Similar arrangementsare also contemplated with respect to the presence of an opening oropenings near the dividing point in catheters having more than two tipsections or more than one dividing point as discussed above, as well aswith respect to the use of protrusions near or around the openings. In asplit-tip catheter having tip sections that are releasably joined, anopening or openings could be placed at intervals along the length of atleast one of the tip sections on an inner surface thereof.

Both tip sections 40 and 50 may include side hole(s) 48 and 58respectively, positioned near their terminal end for enhanced fluid flowinto and out of the tip sections 40 and 50. As should be appreciated byone of skill in the art, many embodiments with respect to the sidehole(s) are possible, including an embodiment with no side holes. Theside hole(s) 48 and 58 can be positioned at various locations around thecircumference of the tip sections 40 and 50 and can be one or several innumber. As shown in the embodiment of FIG. 3, tip section 50 has oneside hole 58 in the side thereof, while tip section 40 has four sideholes spaced in different locations around its circumference and offsetlengthwise from the end opening 44. This particular configuration willbe explored below in reference to FIGS. 7-8.

FIGS. 5-11 illustrate an embodiment of the split-tip catheter of thepresent invention similar to that depicted in FIG. 1. FIG. 5 depicts astraight configuration of a split-tip catheter 100, while FIG. 6 depictsa precurved configuration thereof. In each instance the split-tipcatheter 100 includes a flexible cylindrical catheter tube 114 thatencloses a pair of distinct lumens. In the precurved configuration inFIG. 6, a medial portion of the catheter tube 114 is formed into a bend116. The distal end 128 of the split-tip catheter 100 is bifurcated intoa pair of distal tip sections 124, 126, which are distal to a dividingpoint as discussed above. Each of the tip sections 124, 126 enclose alumen that is respectively continued from the pair of distinct lumensenclosed in the catheter tube 114.

FIGS. 7-8 illustrate the distal tip sections 124, 126 in greater detail.As seen in FIG. 8A, the catheter tube 114 encloses substantially similarD-shaped lumens 120, 122 separated by a planar septum 118. These lumens120, 122 continue on into the distal tip sections 124, 126 respectively,the lumen 120 and associated tip section 124 being the shorter arteriallumen and tip section that is used to withdraw blood from thecardiovascular system for dialysis treatment outside the body, and thelumen 122 and associated tip section 126 being the longer venous lumenand tip section that is used to return blood to the cardiovascularsystem following said dialysis treatment. The arterial tip section 124has a planar surface 130 which faces and is adjacent to a planar surface132 of the venous tip section 126, each of the planar surfaces 130, 132being extensions of the planar septum 118 distal to the dividing point.

Similar to the embodiment shown in FIG. 1, the distal arterial tipsection 124 terminates in an end opening 134 that assumes a semicircularprofile when viewed from the side (FIG. 7). While the lumen 120 isD-shaped and continues through the end opening 134 as such (i.e., thelumen 120 does not taper or enlarge), the side view shows a semicircularprofile due to the edges of the distal end of the arterial tip section124 being rounded. This rounding can be seen in greater detail in FIGS.3 and 4 as well as in FIG. 9, which illustrates a view from the side ofthe arterial tip section 124 identified by line 9-9 in FIG. 7. As shown,an edge 133 of the distal end of the arterial tip section 124 assumes ascalloped configuration as a result of the rounding process. Suchrounding is accomplished by heating with radio frequency (RF) energy,although certainly many other methods of heating could be utilized, butis not limited to the distal end of the arterial tip section 124.Indeed, rounding of the split-tip catheter 100 can be employed onvarious edges and ends thereof.

As mentioned, the D-shape of the arterial tip section 124 is unchangedalong the full length thereof, having planar surface 130 and asemicircular surface 135 that interconnects rounded corners 136 and 137at the lateral ends of the arterial tip section 124 (see FIGS. 8B-8E)and having an end opening 134 as explained above. Arterial tip section124 also has four additional openings for withdrawing blood and formaintaining patency of the lumen 120 and arterial tip section 124 in theevent that the end opening 134 is somehow blocked, the four openingsbeing strategically placed in a longitudinal and circumferential patternfor maximum effect. Specifically, opening 141 can be seen in FIG. 9 (andFIG. 8E), just proximal to the end opening 134 in the semicircularsurface 135, while FIGS. 8B-8D show openings 138, 139 and 140.

In FIG. 8B, opening 138 is through the planar surface 130 of arterialtip section 124, to provide a pathway for blood flow between thearterial and venous tip sections 124, 126, thereby reducing bloodstagnation between the tip sections as discussed above in connectionwith FIGS. 3 and 4 (showing openings adjacent the dividing point 30).Opening 138 is positioned at a longitudinal location proximal to opening141. FIGS. 8C and 8D show openings 139 and 140 respectively through thecorners 136, 137. These side or corner openings 139 and 140 are offsetas can be appreciated from FIG. 7, opening 139 being positioned at alongitudinal location proximal of opening 140, each of which openingsare proximal of opening 141. As depicted, the openings are approximatelyequidistant from one another, or more precisely, the distance betweeneach consecutive opening 138-141 in the arterial tip section 124 issubstantially the same. It should be specifically noted that sideopenings 139 and 140 are multi-planar in nature having portions formedthrough adjacent sides of the catheter (i.e., planar surface 130 andsemicircular surface 135). The multi-planar aspect of the side openings139 and 140 is particularly advantageous with respect to prevention ofocclusion of the arterial lumen due to the remote possibility thateither of the openings could be completely obstructed by a vessel wall.

The positioning of the openings 138-141, as well as the distancetherebetween, is very important with respect to the stated goals offacilitating blood flow and maintaining patency of the catheter. Bypositioning each opening at longitudinal locations offset from oneanother (and in this case approximately equidistant from one another) aswell as at different points around the circumference of the arterial tipsection 124, alternative flow through the arterial tip section 124 ispermitted, preventing thrombus and fibrin formation as well as “sucking”against the vessel wall. More specifically, the offset positioning onfour different sides enables 360° multi-planar flow into the arterialtip section 124 with five effective sides (including the end opening134) for the receipt of blood, such that total occlusion of the arterialtip section 124 is largely eliminated.

The distal venous tip section 126 comprises a proximal portion 142, atransition region 143 and a distal portion 144. The proximal portion 142has a semicircular cross-section similar to the arterial tip section 124that is unchanged from the dividing point to the transition region 143as can be appreciated by viewing the cross-sections shown in FIGS.8B-8E. The planar surface 132 of the venous tip section 126 forms aplanar outer wall of the proximal portion 142 on the side of the venoustip section 126 adjacent to the arterial tip section 124 as explainedabove. A semicircular wall 145 interconnects the lateral ends of thevenous tip section 126 to complete an enclosure of the venous lumen 122.As with the arterial lumen 120, venous lumen 122 is the same size as itscounterpart in the catheter tube 114, although as mentioned above manyvariations are possible.

The transition region 143 connects the proximal portion 142 to thedistal portion 144 and comprises a transition shoulder 156. Thetransition region 143 continuously changes in cross-sectional shapealong its length in transitioning from the semicircular shape of theproximal portion 142 to the circular shape of the distal portion 144. Asshown, the transition shoulder 156 is positioned on a side of the venoustip section 126 adjacent the arterial tip section 124, althoughcertainly other configurations are possible with respect to positioningof the transition shoulder. In addition, configurations includingmultiple transition shoulders are contemplated herein.

The shape of the venous lumen 122 transitions from a D-shape in theproximal portion 142 to a circular shape in the distal portion 144,although the actual cross-sectional area of each shape can bemanipulated to accommodate the particular application (i.e., thecross-sectional area of the distal portion with respect to the proximalportion can increase, decrease or remain substantially equivalent). Inone embodiment, the cross-sectional area for the venous lumen 122 in thedistal portion 144 of the venous tip section 126 is standardized topermit all sizes of the catheter to be tunneled subcutaneously duringimplantation using a single size of tunneling trocar. Thus, thecross-sectional area of the lumen 122 in the proximal portion 142 of thevenous tip section 126 (as well as the cross-sectional area of theproximal portion 142 itself) would vary depending on the size of thecatheter. One possibility, therefore, would include an increase incross-sectional area of the venous lumen 122 from the proximal portion142 to the distal portion 144 of the venous tip section 126. This couldhave advantages in that the discharge velocity of fluid flowing out ofthe end 146 would be reduced, translating into less trauma to the vesseland minimized effects related to shear stress. Of course, it should beapparent to one of skill in the art that various combinations ofcross-sectional shapes and sizes for the venous lumen 122 are possiblealong the length thereof, each of which could enjoy certain advantagesand benefits.

The distal portion 144 has a cylindrical shape with an open end 146 thatis inwardly beveled in the proximal direction toward a plane P₁₃₂. Endopening 148 through the open end 146 is contained in a plane P₁₄₈ thatis shown in FIG. 7 as being oriented at a bevel angle A₁₄₆ to planeP₁₃₂. As a result of the bevel, the end opening 148 is necessarily ovalshaped. The bevel angle A₁₄₆ is shown as approximately 45°, although asstated above in connection with FIGS. 1 and 3, certainly many otherangles are possible, the preferred range being between approximately 25°and 75°. The open end 146 of the venous tip section 126 is rounded(represented by the double line in FIGS. 7 and 9) similar to the end ofthe arterial tip section 124. Referring to FIGS. 8F and 8G, the distalportion 144 of the venous tip section 126 contains two openings 150 and152 that are longitudinally offset from one another. As with the variousopenings described above, openings 150 and 152 can be provided indifferent shapes and sizes and can be positioned at various points alongthe venous tip section 126 to provide additional outlets for the flow ofblood in the event that a blockage occurs.

FIG. 9 is a view of the distal end 128 of the split-tip catheter 100perpendicular to plane P₁₃₂ identified in FIG. 7 by line 9-9. FIG. 10 isan enlarged longitudinal sectional view of the venous tip section 126taken along line 10-10 in FIG. 9, illustrating the transition region143. Various transverse cross-sectional views of venous tip section 126taken along various lines in FIG. 10 are shown in FIGS. 11A-11E. Takentogether, FIGS. 9-11 reveal that in transition region 143 a shoulder 156of continuously longitudinally varying width and height projectsoutwardly from the planar surface 132 of proximal portion 142. Referringto FIG. 9 along with FIGS. 11B-11D, it can be seen that the transitionshoulder 156 has a semicircular cross-sectional aspect with a width anda height above the planar surface 132 that increase from the proximalportion 142 to the distal portion 144 such that shoulder 156 is equal tothe outer diameter of the distal portion 144 at the distal end thereof.

In FIG. 9, shoulder 156 is shown as having linear lateral boundaries 160at which the exterior surface of the shoulder 156 emerges from theplanar surface 132 of venous tip section 126. The lateral boundaries 160intersect at a proximal end 158 of the shoulder 156 and aresymmetrically disposed on opposite sides of the longitudinal axis L₁₂₈of the distal end 128 of the catheter 100. While a specificconfiguration for a transition shoulder is described above, it should beunderstood that other configurations are possible and are contemplatedherein, including, for example, a transition shoulder that decreases inwidth from the proximal portion 142 to the distal portion 144. In anycase, the slope of the shoulder 156 should be positive, although it canbe formed with varying degrees with respect to plane P₁₃₂. Thus,although a positive slope of approximately 5° is shown in FIG. 10,certainly many other possibilities exist that would be within the scopeof the invention.

The shoulder 156 is penetrated obliquely by a somewhatlongitudinally-aligned guidewire aperture 162 that communicates betweenthe exterior of the venous tip section 126 and the venous lumen 122 intransition region 143 and distal portion 144. As clearly seen in FIG. 7,the guidewire 164 is shown extending from arterial lumen 120 through theopen end 134 of arterial tip section 124 and through a guidewireaperture 162 in the transition shoulder 156 into the venous lumen 122 ofthe venous tip section 126, thereby seamlessly connecting the two lumensand tip sections. While threading a guidewire through adjacent tipsections has been preliminarily explored in the prior art, theembodiments disclosed herein are advantageous for several importantreasons. For example, the configuration of the tip sections with respectto one another in combination with a transition shoulder having apositive slope and having a guidewire therethrough affords a streamlinedapproach to connecting the tip sections for ease of delivery to atargeted lumen. In addition, the particular configuration of the innerwall of the guidewire aperture imposes minimal binding stresses on aninsertion guidewire, making the split-tip catheter freely slidablethereon.

Although the examples herein with respect to a guidewire aperture arediscussed in terms of passage of a guidewire therethrough, it will beappreciated by one of skill in the art that an aperture could also beconfigured for passage of a stylet or other instrument, such as theapplicator discussed in U.S. Pat. No. 5,405,341 to Martin, which isincorporated by reference herein. Assuming a larger diameter for astiffening stylet when compared to a standard guidewire, such anaperture would tend to be greater in size than the described guidewireaperture, although certainly many sizes and shapes are possible,including slits.

Referring to the transition shoulder 156 as seen in FIGS. 9-11, theguidewire aperture 162 is formed therein, which is bound by anencircling interior wall 163 that has an inner periphery 165 and anouter periphery 166. The interior wall 163 defines an open cylindricalspace through the transition shoulder 156 and has a longitudinal centralaxis L₁₆₃. The guidewire aperture 162 is formed through the wall of thetransition shoulder 156 at the point through which it is formed at anangle A₁₆₂, which is the measurement between plane P₁₃₂ and longitudinalaxis L₁₆₃. This angle facilitates free slidability of the guidewirethrough the arterial and venous tip sections 124, 126. It is importantto note that many different values for angle A₁₆₂ can be provided, whichshould equally result in the desired slidability with respect to aninsertion guidewire. In particular, it has been discovered that angles(as measured between plane P₁₃₂ and longitudinal axis L₁₆₃) within therange of approximately 0° to 80° provide the desired functionality, withthe optimum range being approximately 0° to 45°. The guidewire aperture162 should be large enough to accommodate passage of a standard 0.038inch guidewire, but not so large as to permit significant back flow ofblood therethrough. In particular, with respect to a 0.038 inchguidewire, it has been discovered that an opening having a radius in therange of approximately 0.039 inch to 0.050 inch is sufficient to allowpassage while minimizing unwanted back flow, with the optimum rangebeing approximately 0.039 inch to 0.041 inch. Certainly, however, otherradius possibilities exist and would be within the scope of theinvention.

In implanting the split-tip catheter 100, the insertion guidewire 164 isthreaded into the catheter 100 by first passing the proximal end thereofinto end opening 148 of the venous tip section 126 and along the venouslumen 122 within the distal portion 144, through the guidewire aperture162 and into the end opening 134 of the arterial tip section 124 whereit is advanced along the full length of arterial lumen 120 to exit thecatheter tube 114 at a proximal end thereof. This course taken by theguidewire 164 is shown in FIG. 7. During implantation into a targetvessel, the distal end 128 of the split-tip catheter 100 is slid in adistal direction along guidewire 164 to a desired location, theguidewire having been previously extended thereto.

In another embodiment of the present invention, a guidewire lumen isformed through the distal portion of the venous tip section, but isseparate from the venous lumen. Thus, in this embodiment the distalportion of the venous tip section comprises two lumens whereas theproximal portion of the venous tip section comprises only one. Thiswould be possible, for example, by providing a transition region similarto that shown in FIG. 7, where the size of the venous tip sectionincreases from proximal to distal portions. In such a configuration, thevenous lumen could remain approximately the same size from the proximalto distal portions with the additional cross-sectional size of thedistal portion of the venous tip section being utilized for anadditional lumen therethrough. The additional lumen ideally would bepositioned at a location in the venous tip section closest in proximityto the arterial tip section (i.e., above the venous lumen in referenceto FIG. 7) so that an instrument passing therethrough will have to bendonly slightly or not at all when passing out of the arterial tip sectionand into the venous tip section.

The presence of an additional lumen permits the use of a stiffeningstylet as described above, without having to increase the size of theguidewire aperture (which may be advantageous to avoid excessive loss ofblood therethrough). Thus, the described embodiment could be formed withor without a guidewire aperture. In the case that a guidewire aperturewas not formed through the transition region, the additional lumen couldaccommodate a guidewire, stiffening stylet or both (in addition topossible other medical instruments). In the case that a guidewireaperture is formed through the transition region, a guidewire andstiffening stylet could be used simultaneously if so desired.

An alternate embodiment of the present invention with respect to theconfiguration of the tip sections is provided in FIGS. 12-14. Asplit-tip catheter 200 is shown having arterial tip section 224 andvenous tip section 226 in FIG. 12, the arterial tip section 224 having aplanar surface 230 extending from a dividing point and venous tipsection 126 having a planar surface 232 in facing relation thereto.Planar surfaces 230, 232 extend from a planar septum 228, which dividesa catheter tube 214 into a pair of distinct lumens that continue intothe arterial tip section 224 and the venous tip section 226 respectivelydistal to the dividing point. Arterial tip section 224 has a terminalend that is cut perpendicular to a longitudinal axis thereof throughwhich an end opening 234 is formed. Arterial tip section 224 containsthree additional openings spaced approximately 120 degrees from oneanother around the circumference of the arterial tip section 224, whichare offset longitudinally approximately equidistant from one another.Openings 238 and 240 can be seen in FIG. 13, while the third opening ispositioned through the planar surface 230 of the arterial tip section224.

The venous tip section 226 has a proximal portion 242, a transitionregion 243 and a distal portion 244 and has an end 246 with an opening248 therethrough (see FIG. 13). Similar to the above-describedembodiment, venous tip section 226 has two openings on opposite sides ofthe distal portion 244, of which opening 252 is shown in FIG. 12. Theseopenings are offset longitudinally along the length of the distalportion 244. The proximal portion 242 has a cross-sectional semicircularshape, while the distal portion 244 has a cross-sectional cylindricalshape. The transition region 243 increases in width and height in adistal direction moving from the proximal portion 242 to the distalportion 244. The transition region 243 includes a pair of longitudinallyextending, parallel reinforcing ridges 254, 256 (FIG. 13), which reducethe bending of the transition region 243 in response to forces imposedon the venous tip section 226 during disposition in the cardiovascularsystem of a patient. Between the reinforcing ridges 254, 256, thesurface of the transition region 243 forms a longitudinally extendingrecess 258 having a floor 260 (FIG. 14) that rises smoothly andcontinuously from the planar surface 232 of the proximal portion 242 tothe curved outer wall of the cylindrical distal portion 244.

In the vicinity of the curved outer wall of the cylindrical distalportion 244, the floor 260 of the recess 258 is penetrated by aguidewire aperture 262 that communicates between the exterior of thevenous tip section 226 and the venous lumen 222 (FIG. 14). The planarsurface 232 of venous tip section 226 is extended to a longitudinalpoint where the floor 260 of the transition region 243 merges with thewall of the cylindrical distal portion 244 so that an overhead view(FIG. 13) does not reveal the guidewire aperture 262. This forms a ledgeof sorts that, in combination with parallel reinforcing ridges 254, 256,directs the guidewire 264 and maintains it in position as the split-tipcatheter 200 is slid therealong into the cardiovascular system of thepatient. To prepare for use, the insertion guidewire 264 is threadedinto the split-tip catheter 200 by first passing the proximal endthereof into end opening 248 of the venous tip section 226 and along thevenous lumen 222 within the distal portion 244, through the guidewireaperture 262 and into the end opening 234 of the arterial tip section224 where it is advanced along the full length of arterial lumen 220 toexit the catheter tube 214 at a proximal end thereof.

While the split-tip catheters 100 and 200 are configured to allow forsheathless delivery into a cardiovascular system of a patient due to thepresence of guidewire apertures 162 and 262, respectively, animprovement to related to the sheathed delivery of split-tip cathetersis illustrated in FIGS. 15-20. With respect to FIGS. 15A-15B, a priorart split-tip catheter 310 is shown within a delivery sheath 370 toillustrate a potential problem solved by the present invention. Tipsections 340 and 350 are shown distal to dividing point 330. Each tipsection 340 and 350 transitions at a distal end from a D-shaped lumen toa lumen that is circular in cross-section and each has a terminal endthat is cut perpendicular to a longitudinal axis thereof. As shown inFIG. 15A, edges 348 and 358 located at the terminal ends of tip sections340 and 350 abut the inside surface 372 of the sheath 370. Thus, asshown in FIG. 15B, when the catheter 310 is moved out of delivery sheath370 and into a blood vessel in a direction 390, the opposing frictionforce 392 forces the tip sections in an outward direction into thesheath 370 as indicated by arrows 394 and 396. This movement of the tipsections 340 and 350 into the inside surface 372 of the delivery sheath370 causes the edges 348 and 358 to catch or “snag” on the insidesurface 372, resulting in difficult insertions or other attendantproblems with the delivery process.

One potential method for alleviating this problem would be to use alarger diameter sheath so that the tip sections will have a greaterdistance to travel to come in contact with the inside surface of thesheath when the friction forces act on the tip sections, therebyminimizing the chance of a snag. However, this solution is flawed inthat snags are still possible and the risk of air embolism is amplifieddue to the increase in surface area between the catheter and the sheath.FIG. 16 illustrates one embodiment of the present invention thataddresses a solution to the sheathed delivery problems described. Inparticular, a multi-lumen catheter 410 having tip sections 440 and 450distal to a dividing point 430 is shown, the catheter 410 beingpositioned within delivery sheath 370 having an inside surface 372. Toprevent the terminal ends of the tip sections from catching or“snagging” on the inside surface 372 of the delivery sheath 370, afriction reducing structure is provided.

In FIG. 16, the friction reducing structure is illustrated as a slightprotrusion or “bump” of material 480, which is positioned on the outsidesurface of tip sections 440 and 450 near the terminal ends thereof.Thus, as friction forces tend to push the tip sections outward from acentral axis of the catheter 410 upon removal from the sheath 370 andinto the blood vessel (as described above), the protrusion 480 providesa buffer to prevent edges 448 and 458 from coming into direct contactwith the inside surface 372 of the delivery sheath 370 and also providesa relatively small surface area for contact. Of course, there are manyways for reducing friction utilizing the protrusions as discussed above,including using a plurality of protrusions on the catheter tip sectionsin various locations along their length. However, the embodiment shownin FIG. 16 is advantageous due to the small surface area utilized, theease of manufacture and the wide-ranging applicability for use with avariety of catheter configurations.

FIG. 17 illustrates an alternate embodiment for reducing friction,wherein each of the tip sections 440 and 450 have a ring of material 482around an end thereof distal to the dividing point 430. The rings 482,similar to the protrusions 480, distance the sharp edges of the tipsections 440 and 450 from the inside surface of a delivery sheath andtherefore reduce friction forces associated with the delivery of asplit-tip catheter from a delivery sheath and into a patient's vessel.The rings 480 may also act as a buffer of sorts for the tip sections 440and 450 while within a patient's vessel by acting to keep the distalends from coming into direct contact with the walls of the vessel.

Another embodiment for reducing friction comprises an inflatablematerial being positioned on one or more points along the catheter. Inthis embodiment, a small inflation lumen is positioned on the inner orouter of either or both arterial or venous lumens, extending from theproximal end of the catheter to the point on the catheter containing theinflatable material. When the catheter is positioned for delivery withina delivery sheath, air, gas or liquid is transmitted through theinflation lumen to the inflatable material, expanding said material intocontact with the inner of the delivery sheath. Preferably, theinflatable material would be positioned close to the distal end of thecatheter on the tip sections so that the goal of preventing the edges ofthe tip sections from coming into contact with the inside surface of thedelivery sheath can be realized. Alternatively or in addition to thegoal of reducing friction, placement of inflatable material on variousareas on a surface of the catheter could act to remove clots and/orfibrin through the inflation thereof (i.e., by knocking the formationsoff of the surface upon inflation). Referring now to FIG. 18, thecatheter 410 has balloons 444 and 454 positioned near the distal ends ofthe tip sections 440 and 450, respectively, and are connected torespective inflation lumens 442 and 452. Balloon 444 is shown in itsinflated, expanded position for ready contact with the inside surface ofa delivery sheath such as delivery sheath 370. Balloon 454 is shown inits deflated, unexpanded position.

In yet another embodiment of the present invention, a friction reducingstructure is provided by positioning a ridge or ridges 380 on the insidesurface 372 of delivery sheath 370, as shown in FIGS. 19 and 20. As withthe embodiments involving protrusions positioned on the surface of thecatheter, the ridge(s) 380 prevent direct contact of any sharp edges ofa tip section with the inside surface 372 of the delivery sheath 370.The ridges 380 can be formed from a mound or bump of material or couldalso be formed from balloons as described with reference to FIG. 18.

It is noted that although the delivery problems presented with referenceto FIGS. 15A and 15B are certainly more likely to be presented interminal ends such as those shown, other tip configurations could alsopresent problems with snags or tears, which problems can be minimizedthrough any of the friction reducing structures described above.

Referring now to FIGS. 21A-21H, an improvement to prior art split-tipcatheters that are releasably joined or “splittable” distal to thedividing point is illustrated, wherein increasing separation force isrequired to separate the tip sections from one another. An increasingseparation force as used herein means that the bond strength between thetip sections of the catheter will be greater as measured from a distalend toward the dividing point. However, the releasably joined orsplittable region need not extend over the entire length of the tipsections and need not begin adjacent the dividing point. Thus, while thereleasably joined or splittable region could extend the entire distancefrom a terminal end of one or more tip sections to the dividing point,it could also span a much shorter distance along the tip sections suchthat the releasably joined or splittable region is not adjacent eitherthe dividing point or a terminal end of one or more tip sections.

The creation of an increasing separation force between tip sections canbe accomplished in a variety of ways, as one of skill in the art shouldappreciate, some of which ways will be described in detail below (thoughcertainly many others would be within the scope of the presentinvention). In addition, although the examples herein are described withrespect to an increasing separation force, the production of adecreasing separation force is also contemplated, the implementation ofwhich should be apparent to one of skill in the art in light of thediscussion regarding an increasing separation force. Further, thediscussion with respect to the separation of splittable tip sectionsherein encompasses both permanent and temporary (i.e., releasablyjoined) separation.

The concept of increasing the required separation force to separate tipsections from one another is illustrated by way of example, notlimitation, through the graphs in FIG. 21A and 21B. In each of thesegraphs, the y-axis represents the separation force F required toseparate the tip sections from one another and the x-axis represents theposition P along the joined portion of the tip sections as measuredbeginning at a distal end thereof and moving toward the dividing point.The points on the graph, P₁, P₂ and P₃ are points along the joinedportion of the tip sections (as further illustrated in FIGS. 21C-21H),having corresponding increasing separation forces F₁, F₂ and F₃. Whilethree distinct points are shown, certainly any number of points arepossible and are contemplated herein. The point P_(F) corresponds toF_(E), which is the excessive separation force as defined above.

The graphs in FIG. 21A and 21B illustrate two possibilities for varyingthe separation force along the length of a split-tip catheter, whereinsaid force is increasing as a function of position of joined portion ofthe tip sections when measured beginning at the a distal end thereof andmoving in a proximal direction toward the dividing point. FIG. 21Aillustrates a straight line continuous separation force, while FIG. 21Billustrates an incremental separation force accomplished in discreetsteps, meaning that the change in force ΔF is too great for spontaneoussplitting.

One embodiment of tip sections having an increasing separation force isillustrated in FIG. 21C, where fusion points are shown on an innersurface 512 of a tip section 510 of a catheter 500 along a predeterminedlength L₁ (tip section 510 is shown as separated from an adjacent tipsection 520 for purposes of illustration). As used herein, the term“fusion point” refers to a fused surface area between a splittableinterface and should not be restricted to a “point” per se. Thus,referring to FIG. 21C, the fusion points would be fused surface areasbetween the inner surface 512 of the tip section 510 and the innersurface 522 of the tip section 520 (even though the tip sections areshown as separate). In this embodiment, the fusion points willpreferentially detach upon application of a consistent force relative tothe surface area of the fusion.

As shown in FIG. 21C, the fusion points of a first zone 530, formedbetween P₁ and P₂, are lighter in shading than the fusion points of asecond zone 540, formed between P₂ and P₃, which in turn are lighter inshading than the fusion points of a third zone 550, formed between P₃and P_(F). While the shading is shown to be uniform within each zone,one contemplated variation would be to increase the shading (i.e.,fusion strength) within each zone when moving toward a higher number(i.e., P₁ to P₂) as shown in FIG. 21E. In effect, such a configurationcreates subzones or additional fusion zones. The darker shaded fusionpoint in these embodiments represents a fusion point having a greaterbond strength, meaning that the fusion points of the third zone 550would have a greater bond strength than those of the second zone 540,which in turn would have a greater bond strength than those of a firstzone 530. This effect could be accomplished, for example, by utilizingdifferent adhesives or solvents for different zones, using variousdilutions of adhesives or solvents for different zones, utilizingvarying application times of the adhesive or solvent for different zonesor using variable pressure upon bonding (more force on one end thananother) for different zones, as will be described in greater depthbelow.

In addition to greater bond strength for the fusion points in adjacentzones in FIG. 21C, the number (density) of the fusion points areincreased in each successive zone and within each fusion zone, with thethird zone 550 having a greater number of fusion points than the secondzone 540, in turn having a greater number of fusion points than thefirst zone 530. With a greater number of fusion points comes anincreased surface area for fusion between inner surface 512 of the tipsection 510 and inner surface 522 of the tip section 520, therebyincreasing the required separation force when moving from the distal endof the catheter 500 to the proximal end of the catheter 500. Also, withthe number of fusion points progressively increasing within each fusionzone, a continuous configuration is created. The combination of greaterbond strength in fusion points between adjacent fusion zones andincreasing number of fusion points within each fusion zone creates ahybrid continuous/stepped configuration, wherein the separation forceincreases within each zone following a continuous curve (as representedin FIG. 21A) and increases in a stepped manner with respect to adjacentzones (as represented in FIG. 21B).

FIG. 21D illustrates an embodiment of the present invention followingthe stepped configuration represented by FIG. 21B, wherein the number offusion points within each fusion zone is uniform as is the bond strengthof the fusion points within each fusion zone, but the bond strength ofthe fusion points is greater in each successive fusion zone as in FIG.21C. FIG. 21E follows the continuous configuration represented by FIG.21A, wherein the number of fusion points is uniform within each fusionzone, but the bond strength of the fusion zones is progressivelyincreased as between fusion zones and within each fusion zone (i.e., thebond strength of the fusion points in the first fusion zone 530 areprogressively increased as are those in the second fusion zone 540 andthe third fusion zone 550). FIG. 21F follows a stepped configuration asthe bond strength of the fusion points is the same in all fusion zones,but the number of fusion points is increased in each successive fusionzone (the number of fusion points is uniform within each zone). In FIG.21G, the bond strength of the fusion points is the same in all fusionzones, as is the number of fusion points, but the size of the fusionpoints is increased in successive fusion points, creating a steppedconfiguration.

Yet another embodiment of the present invention with respect to theestablishment of an increasing separation force is illustrated in FIG.21H, where the zones themselves increase in size. A catheter 600 isshown with tip sections 610 and 620, having four discrete and separatefusion zones, indicated by shading (the shading representing fusionpoints), on inner surface 612. A first zone 630 is smaller and thereforehas less surface area for adhesion than a second zone 640, which in turnis smaller than a third zone 650, which in turn is smaller than a fourthzone 660. In this embodiment, there are free zones that do not havefusion points thereon, positioned in between each of the four statedzones. The first, second, third and fourth zones 630-660 can consist offusion points as described above, in any combination thereof. Thus, forexample, the first zone 630 could have a certain density of fusionpoints, while the second zone 640 could have a somewhat higherseparation force created by a larger size of fusion points.

A further embodiment of a catheter having a variable separation force isillustrated in FIG. 21I. In this figure, a catheter 700 is shown withtip sections 710 and 720, having a continuous fusion zone 730 thatincreases in size along L₁ from a distal end to a dividing point. Ofcourse, one of skill in the art will appreciate the myriad ofpossibilities within the scope of the present invention with respect tothe varying of fusion points and establishment of an increasingseparation force in light of the embodiments illustrated herein.

Methods for producing the desired effects with respect to theestablishment of an increasing separation force, as described above,include (but are not limited to) utilizing constant separation stresswith a variable area and using a variable separation stress with aconstant area. Realization of these embodiments can be accomplishedthrough many different bonding techniques, a few of which are describedbelow.

With respect to constant separation stress over a variable area, a firstpotential technique is the use of adhesive bonding in creating a varyingpattern of adhesive to join the tip sections of a split-tip catheter.Types of adhesive which could be used include epoxy and cyanoacrylates,although certainly other comparable adhesives would also be suitable.This idea has been explored above, for example, with respect to varyingthe density of the fusion points and the size of the fusion points. Asecond technique is the use of solvent bonding in creating a varyingpattern of solvent to join the tip sections of a split-tip catheter.Examples of the types of solvents that could be employed includeTecoflex® 1-MP (Thermedics), methyl ethyl ketone (MEK), cyclohexanon andalcohol, though certainly others could be used. A third technique is theuse of thermal welding, in which heat can be used to join the tipsections of a split-tip catheter. A fourth technique is the use of RFenergy to fuse the tip sections of a split-tip catheter. Finally, afifth technique is the use of variable extrusion where surface area of ajoining web could be increased between two lumens during the extrusionprocess.

In reference to variable separation stress over a constant area, thetechniques above would be applicable in a different way. Specifically,in an adhesive bonding technique, the concentration of the adhesivecould be varied to produce the variable bond strength. This idea hasbeen explored above with respect to varying the type of adhesive used.In a solvent bonding technique, the solvent could be varied or thepressure utilized to join the tip sections could be varied. In a thermalwelding technique, the temperature or dwell time could be varied. In anRF fusion technique, variable RF energy could be utilized. Finally, in avariable extrusion technique, pressure, temperature or dwell time couldbe varied during the extrusion process.

Still another embodiment of the present invention with respect to theestablishment of an increasing separation force is illustrated in FIGS.22A and 22B, where the separation force is created by twisting thecatheter upon formation thereof. FIG. 22A illustrates a gradual twistbeing applied to the catheter, while FIG. 22B illustrates a more abrupttwist over a shorter length. The twisting configuration imparts avariable separation force along the length of the catheter, increasingas measured from the distal end to the proximal end. For example, if aconstant separation force is applied linearly to tip sections in acatheter having a 90° twisted septum, the force F a distance L away(i.e., the distal end of the catheter) would diminish to zero in thedirection needed to continue the splitting, because F would be resolvedin the tensile direction of the septum if the tube could not rotate. Onthe other hand, were the tube able to rotate, the force would notdiminish to zero but would be reduced by the energy required to rotatethe tube 90°.

The twisting action can be implemented in a number of ways, includingemploying a mandrel having a desired twist, which when inserted into astill warm tube, imparts the twist to the tube during cooling andutilizing a series of mandrels to force a previously straight tube intoa desired twisted pattern, wherein heat is applied to reset the tubingconfiguration. Another technique would be to employ an extrusion diehaving a preset desired twist so that the twist is imparted to thecatheter during formation thereof. Referring back to FIGS. 22A and 22B,the gradual twist 820 of the catheter 810 permits slow increase inresistance by transferring the splitting energy into rotational force ifthe catheter 810 is sufficiently flexible to twist when split.Differently, the abrupt twist 920 imparted to catheter 910 creates atactile “positive stop,” which notifies a user when a predeterminedposition along the length of the catheter 910 has been attained.Multiple twists could also be employed to provide a tactile measurementmethod for the user, and to provide an incremental separation force asdescribed above in FIG. 21B.

Although improvements to the functioning and usability of a split-tipcatheter have been presented separately herein, the improvementsdescribed above (for example, openings positioned near a dividing pointof a split tip catheter, positioning of a guidewire aperture in a venoustip section, configuration of arterial and venous tip sections withrespect to one another, friction reducing structures provided on adelivery sheath and/or a catheter, varying the separation force requiredto separate tip sections from one another, etc.) should not beconsidered exclusive and instead should be considered for use inconjunction with one another.

The present invention has been described above in terms of certainpreferred embodiments so that an understanding of the present inventioncan be conveyed. However, there are many alternative arrangements for amulti-lumen catheter not specifically described herein but with whichthe present invention is applicable. Although specific features havebeen provided, the multi-lumen catheter of the present invention wouldequally be embodied by other configurations not specifically recitedherein. The scope of the present invention should therefore not belimited by the embodiments illustrated, but rather it should beunderstood that the present invention has wide applicability withrespect to catheter systems generally. All modifications, variations, orequivalent elements and implementations that are within the scope of theappended claims should therefore be considered within the scope of theinvention.

1. A method of producing a variable separation force between adjacentinner surfaces of tip sections distal to a dividing point in a split-tipcatheter, comprising creating two or more distinct fusion zones betweenthe inner surfaces, each fusion zone including a different bondstrength.
 2. The method according to claim 1, wherein the fusion zonesextend from a distal end of at least one of the inner surfaces to thedividing point.
 3. The method according to claim 1, wherein the creatingstep includes progressively increasing the bond strength of the fusionzones in a proximal direction.
 4. The method according to claim 1,wherein the creating step includes the step of applying a pattern ofadhesive to each fusion zone.
 5. The method according to claim 4,wherein the applying step includes disposing a plurality of fusionpoints in each pattern of adhesive, each fusion zone including adifferent number of fusion points.
 6. The method according to claim 5,wherein the disposing step includes progressively increasing the numberof fusion points in the fusion zones in a proximal direction.
 7. Themethod according to claim 6, wherein the disposing step includesprogressively increasing the number of fusion points within each fusionzone from a distal end to a proximal end of the fusion zone.
 8. Themethod according to claim 4, wherein the applying step includesdisposing a plurality of fusion points in each pattern of adhesive, eachfusion zone including a different size of fusion points.
 9. The methodaccording to claim 8, wherein the disposing step includes progressivelyincreasing the size of the fusion points in the fusion zones in aproximal direction.
 10. The method according to claim 1, wherein thecreating step includes the step of applying a different type of adhesiveto each of the fusion zones.
 11. The method according to claim 10,wherein the bond strength of each type of adhesive progressivelyincreases in a proximal direction.
 12. The method according to claim 1,wherein the creating step includes the step of applying a pattern ofsolvent to at least one of the inner surfaces, each of the fusion zonesincluding a different pattern of solvent.
 13. The method according toclaim 1, wherein the creating step includes utilizing a thermal weldingtechnique.
 14. The method according to claim 1, wherein the creatingstep includes utilizing radio frequency energy.
 15. The method accordingto claim 1, wherein the creating step includes extruding the split-tipcatheter with a joining web positioned between the inner surfaces,wherein the surface area of the joining web increases in a proximaldirection.
 16. The method according to claim 1, wherein the creatingstep includes the step of twisting the split-tip catheter upon formationthereof.
 17. The method according to claim 16, wherein the twisting stepincludes positioning a twisted mandrel into a warm tube.
 18. A method ofjoining tip sections of a split-tip catheter to impart a variableseparation force, comprising creating a continuous fusion zone betweenthe tip sections, the fusion zone increasing in size in a proximaldirection.
 19. A method of joining tip sections of a split-tip catheterto impart a variable separation force, comprising creating two or morefusion zones between the tip sections, the fusion zones including aprogressively greater bond strength in a proximal direction.
 20. Themethod according to claim 19, wherein the fusion zones progressivelyincrease in size in a proximal direction.